Resistance change memory

ABSTRACT

A resistance change memory includes a memory cell array comprising memory cells including magnetic tunnel junction (MTJ) elements; a write and read circuit which performs a write operation and a read operation for the memory cells; a temperature sensor which outputs temperature information corresponding to a temperature of the memory cell array; and a memory controller which controls the write operation and the read operation by the write and read circuit in response to the temperature information, such that a first time period from a write command input to a pre-charge command input is variable according to the temperature information, while a second time period from an active command input to the pre-charge command input is fixed constant regardless of the temperature information.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. Ser. No. 14/482,904, filedSep. 10, 2014, which claims the benefit of U.S. Provisional ApplicationNo. 61/952,696, filed Mar. 13, 2014, the entire contents of both ofwhich are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a resistance changememory to store data by using the change of the resistance value of amemory element.

BACKGROUND

Recently, attention has been focused on semiconductor memories that use,as a memory device, a nonvolatile memory such as a resistance changememory (e.g., a magnetoresistive random access memory: MRAM, a phasechange random access memory: PRAM, or a resistive random access memory:ReRAM).

In the resistance change memory, the change of its resistance valuecaused by the application of a current (or voltage) is used to determinewhether data is “1” or “0”.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a diagram showing the configuration of an MRAM according to anembodiment;

FIG. 2 is a diagram showing the detailed configuration of the MRAMaccording to the embodiment;

FIG. 3 is a block diagram of a memory cell array according to theembodiment;

FIG. 4 is a circuit diagram of one group GP included in the memory cellarray according to the embodiment;

FIG. 5 is a sectional view of an MTJ element according to theembodiment;

FIG. 6 is a circuit diagram of an example of a temperature sensoraccording to the embodiment;

FIG. 7 is a graph showing the current characteristics of the example ofthe temperature sensor according to the embodiment;

FIG. 8 is a circuit diagram of another example of a temperature sensoraccording to the embodiment;

FIG. 9 is a graph showing the current characteristics of the otherexample of the temperature sensor according to the embodiment;

FIGS. 10 and 11 are diagrams showing a write operation and a readoperation in the MRAM according to the embodiment; and

FIG. 12 is a diagram showing a write operation and a read operation inan MRAM according to a comparative example.

DETAILED DESCRIPTION

Hereinafter, a resistance change memory according to an embodiment willbe described with reference to the drawings. In the followingdescription, the same reference signs are provided to components havingthe same functions and configurations, and repeated explanations aregiven only when necessary. Embodiments shown below illustrate devicesand methods which embody the technical concepts of the embodiments, andthe materials, shapes, structures, and locations of the components arenot specified as below.

In general, according to one embodiment, a resistance change memorycomprises a memory cell array, a write and read circuit, a temperaturesensor, and a memory controller. The memory cell array comprises memorycells including magnetic tunnel junction (MTJ) elements. The write andread circuit performs a write operation and a read operation for thememory cells. The temperature sensor outputs temperature informationcorresponding to a temperature of the memory cell array. The memorycontroller controls the write operation and the read operation by thewrite and read circuit in accordance with the temperature information.

An MRAM is described as an example of the resistance change memory inthe embodiment below.

[1] Configuration of MRAM

FIG. 1 is a diagram showing the configuration of the MRAM according tothe embodiment.

According to the present embodiment, an MRAM 10 and a memory controller20 are provided. The MRAM 10 includes a memory cell array 11, aread/write circuit 12, a temperature sensor 13, an interface 14, and acontroller 15. The MRAM 10 can store data in memory cells disposed inthe memory cell array 11. The memory controller 20 controls theoperation of the MRAM 10. A CPU 30 may be further connected to thememory controller 20 as an external system. The CPU 30 sends signals tothe memory controller 20 and receives signals from the memory controller20.

The detailed configuration of the MRAM according to the embodiment isshown in FIG. 2.

The memory cell array 11 includes the memory cells. Here, the memorycells have magnetoresistive effect elements, for example, magnetictunnel junction (MTJ) elements as resistance change elements. Theconfiguration of the memory cells will be described in detail later.

The read/write circuit 12 comprises a sense amplifier (S/A) 12A, a writebuffer (W/B) 12B, an error checking and correcting (ECC) circuit 12C, apage buffer (P/B) 12D, and a row decoder 12E.

[1-1] Configuration of Memory Cell Array

FIG. 3 is a block diagram of the memory cell array 11. The memory cellarray 11 comprises groups GP. In FIG. 3, four groups GP0 to GP3 areshown by way of example. Each group GP is a unit for independentlyperforming a data write operation and a data read operation (interleaveprocessing and parallel processing). While the interleave processing isperformed by four columns YA, YB, YC, and YD corresponding to the fourgroups GP0 to GP3 in the following explanation by way of example, thenumber of groups GP (number of columns) can be designed to be anynumber. Each group GP comprises pages.

FIG. 4 is a circuit diagram of one group GP included in the memory cellarray 11. The group GP is composed of memory cells MC arrayed in amatrix form. Word lines WL0 to WLm−1, bit lines BL0 to BLn−1, and sourcelines SL0 to SLn−1 are arranged in the group GP. A memory cell group forone row of groups GP, that is, for one page is connected to one wordline WL. One column of groups GP is connected to a pair comprising onebit line BL and one source line SL. The common word lines WL0 to WLm−1are connected to the groups GP0 to GP3. m and n are natural numbersequal to or more than 1.

The memory cell MC comprises, for example, a magnetic tunnel junction(MTJ) element RE and a select transistor ST. The select transistor STcomprises, for example, an n-channel MOS field effect transistor.

One end of the MTJ element RE is connected to the bit line BL, and theother end of the MTJ element RE is connected to the drain of the selecttransistor ST. The source of the select transistor ST is connected tothe source line SL. Moreover, the gate of the select transistor ST isconnected to the word line WL.

[1-2] Structure of MTJ Element

Now, one example of the structure of the MTJ element RE is described.FIG. 5 is a sectional view of the MTJ element RE. The MTJ element REcomprises a bottom electrode 40, a storage layer (also referred to as afree layer) 41, a nonmagnetic layer (tunnel barrier layer) 42, areference layer (also referred to as a fixed layer) 43, and a topelectrode 44 that are stacked in the order above. The storage layer 41and the reference layer 43 may be stacked in reverse order.

The storage layer 41 and the reference layer 43 are made of aferromagnetic material. An insulating material such as MgO is used asthe tunnel barrier layer 42.

The storage layer 41 and the reference layer 43 have perpendicularmagnetic anisotropy, and their directions of easy magnetization areperpendicular directions. The magnetization directions of the storagelayer 41 and the reference layer 43 may be in-plane directions.

The magnetization direction of the storage layer 41 is variable(inverted). The magnetization direction of the reference layer 43 isinvariable (fixed). The reference layer 43 is set to have sufficientlyhigher perpendicular magnetic anisotropic energy than the storage layer41. The magnetic anisotropy can be set by adjusting materialconstitution and thickness. Thus, a magnetization inversion current forthe storage layer 41 is lower, and a magnetization inversion current forthe reference layer 43 is higher than that for the storage layer 41. Asa result, it is possible to obtain an MTJ element RE that comprises thestorage layer 41 variable in magnetization direction and the referencelayer 43 invariable in magnetization direction for a predetermined writecurrent.

According to the present embodiment, a spin-transfer torque writingmethod is used so that a write current is directly passed through theMTJ element RE, and the magnetization state of the MTJ element RE iscontrolled by this write current. The MTJ element RE can take one of alow-resistance state and a high-resistance state depending on whetherthe magnetizations of the storage layer 41 and the reference layer 43are parallel or antiparallel.

If a write current running from the storage layer 41 to the referencelayer 43 is passed through the MTJ element RE, the magnetizations of thestorage layer 41 and the reference layer 43 are parallel. In thisparallel state, the resistance value of the MTJ element RE is lowest,and the MTJ element RE is set to the low-resistance state. Thelow-resistance state of the MTJ element RE is determined as, forexample, data “0”.

On the other hand, if a write current running from the reference layer43 to the storage layer 41 is passed through the MTJ element RE, themagnetizations of the storage layer 41 and the reference layer 43 areantiparallel. In this antiparallel state, the resistance value of theMTJ element RE is highest, and the MTJ element RE is set to thehigh-resistance state. The high-resistance state of the MTJ element REis determined as, for example, data “1”.

Consequently, the MTJ element RE can be used as a storage elementcapable of storing one-bit data (binary data). Any resistance state ofthe MTJ element RE and any allocation of data can be set.

When data is read from the MTJ element RE, a read voltage is applied tothe MTJ element RE, and the resistance value of the MTJ element RE isdetected in accordance with a read current running through the MTJelement RE at the moment. This read voltage is set to a value that issufficiently lower than a threshold at which the magnetization isinverted by spin injection.

[1-3] Configuration of Read/Write Circuit

In FIG. 2, the sense amplifier 12A, the write buffer 12B, the ECCcircuit 12C, and the page buffer 12D are provided for each of thecolumns YA, YB, YC, and YD. In the following explanation, when the senseamplifier 12A, the write buffer 12B, the ECC circuit 12C, and the pagebuffer 12D are mentioned in this way, this means that the columns YA toYD have a common configuration. On the other hand, the reference signsYA to YD are given only when the columns YA to YD need to bedistinguished from one another.

The row decoder 12E is connected to the word lines WL0 to WLm−1. The rowdecoder 12E selects one of the word lines WL in accordance with a rowaddress.

The sense amplifier 12A is connected to the bit lines BL0 to BLn−1. Thesense amplifier 12A of, for example, a current detecting type compares acell current running through the selected memory cell via the bit lineBL with a reference current, and thereby detects and amplifies the datain the selected memory cell. During reading, the source lines areclamped to a ground voltage VSS by the write buffer 12B. An output fromthe write buffer 12B to the bit line is set to a Hi-Z state (highimpedance state) to avoid conflicting with the operation of the senseamplifier.

The write buffer 12B is connected to the bit lines BL0 to BLn−1 and thesource lines SL0 to SLn−1. The write buffer 12B writes data into theselected memory cell via the bit line BL and the source line SL.

The ECC circuit 12C performs the ECC operation to detect an error in theread data and correct the error. That is, when data is written into thememory cell array 11, the ECC circuit 12C uses write data to generate anerror correcting code, and adds this error correcting code to the writedata. The error correcting code is written into a parity bit area in thememory cell array 11. When data is read from the memory cell array 11,the ECC circuit 12C uses the error correcting code read from the paritybit area to detect and correct an error. The error correcting code doesnot need to be read to the outside, and is therefore not read into thepage buffer 12D. For such processing, the ECC circuit 12C comprises anECC encoder and an ECC decoder.

The page buffer 12D holds the read data sent from the ECC circuit 12C.The page buffer 12D also holds the write data sent from the input/outputinterface circuit 14. The page buffer 12D comprises a read page bufferfor holding read data, and a write page buffer for holding write data.

[1-4] Configurations of Interface and Controller

The input/output interface circuit 14 is connected to an externalsystem, and inputs/outputs data to/from the external system. Theinput/output interface circuit 14 sends input data input from theexternal system to the page buffer 12D as write data. The input/outputinterface circuit 14 also outputs the read data received from the pagebuffer 12D to the external system as output data.

The controller 15 has overall control of the operations of the senseamplifier 12A, the write buffer 12B, the ECC circuit 12C, the pagebuffer 12D, the row decoder 12E, and the interface 14. The controller 15receives an address (including a row address and a column address), andcontrol signals such as a clock CLK and a command from the memorycontroller 20. The controller 15 supplies various control signals andvarious voltages to the sense amplifier 12A, the write buffer 12B, theECC circuit 12C, the page buffer 12D, the row decoder 12E, and theinterface 14, and thereby controls the operations of these circuits.

[1-5] Configuration of Temperature Sensor

The temperature sensor 13 is disposed in the vicinity of the memory cellarray 11, and detects the temperature of the environment of the memorycell array 11, and then outputs temperature information STIcorresponding to the detected temperature. The memory controller 20receives the temperature information STI from the temperature sensor 13,and outputs a control signal for controlling the write operation and theread operation in the MRAM 10 to the controller 15 in accordance withthe temperature information STI. The controller 15 receives the controlsignal from the memory controller 20, controls the read/write circuit 12in accordance with the control signal, and performs the write operationand the read operation for the memory cell array 11. The write operationand the read operation will be described in detail later.

Now, one example of the configuration of the temperature sensor 13 isdescribed. FIG. 6 is a circuit diagram of the temperature sensor 13according to the embodiment. FIG. 7 is a graph showing thevoltage-current characteristics of the temperature sensor 13.

As shown in FIG. 6, the temperature sensor 13 comprises a comparatorCP1, resistances R1, R2, and R3, p-channel MOS field effect transistorsTR1 and TR2, and a diode D1. A current running through the resistance R3is Ires, and a current running through the diode D1 is Idio.

FIG. 7 shows the current characteristics of the current Ires and thecurrent Idio in a low-temperature state and a high-temperature state.This graph shows the level relation between voltages Vx and Vr in thelow-temperature state and the high-temperature state.

When the memory cell array 11 is in the low-temperature state, thevoltage Vx is lower than the voltage Vr in FIG. 7. As a result, anoutput out becomes “low (L)”. Therefore, when detecting that the memorycell array 11 is in the low-temperature state, the temperature sensor 13outputs “L” as the temperature information STI.

When the memory cell array 11 is in the high-temperature state, thevoltage Vx is higher than the voltage Vr in FIG. 7. As a result, theoutput out becomes “high (H)”. Therefore, when detecting that the memorycell array 11 is in the high-temperature state, the temperature sensor13 outputs “H” as the temperature information STI.

In response to “L” or “H” as the temperature information STI from thetemperature sensor 13, the memory controller 20 controls the writeoperation and the read operation in accordance with “L” or “H”.

Although the temperature sensor 13 detects the two temperature rangesincluding the low temperature and the high temperature in the exampleshown here, the temperature sensor 13 may detect three temperatureranges including the low temperature, the high temperature, and a mediumtemperature higher than the low temperature and lower than the hightemperature. Moreover, the temperature sensor 13 may detect four or moretemperature ranges. In this case, the circuits can be configured byadding comparators, resistances, and condensers.

One example of the configuration of the temperature sensor 13 whichdetects the three temperature ranges is shown below. FIG. 8 is a circuitdiagram of the temperature sensor 13 which detects the three temperatureranges. FIG. 9 is a graph showing the voltage-current characteristics ofthe temperature sensor 13.

As shown in FIG. 8, the temperature sensor 13 comprises comparators CP1and CP2, resistances R1, R2, R3, R4, and R5, p-channel MOS field effecttransistors TR1 and TR2, and a diode D1. A current running through theresistance R5 is Ires, and a current running through the diode D1 isIdio.

FIG. 9 shows the current characteristics of the current Ires and thecurrent Idio in temperature conditions: the low temperature, the mediumtemperature, and the high temperature. This graph shows the levelrelation between voltages Vx, Vr<0>, and Vr<1> in each temperaturecondition. This level relation can be easily obtained by adjusting theresistance ratio of R1, R2, R3, and R4 so thatVr<0>=R2*VDD/(R1+R2)<Vr<1>=R3*VDD/(R3+R4).

When the memory cell array 11 is in a low-temperature state, the voltageVx is lower than the voltages Vr<0> and Vr<1> in FIG. 8. As a result,both outputs out<1> and out<0> become “low (L)”. Therefore, whendetecting that the memory cell array 11 is in the low-temperature state,the temperature sensor 13 outputs “LL” as the temperature informationSTI.

When the memory cell array 11 is in the medium-temperature state, thevoltage Vx is higher than the voltage Vr<0> and lower than Vr<1> in FIG.8. As a result, the output out<1> becomes “low (L)”, and the outputout<0> becomes “high (H)”. Therefore, when detecting that the memorycell array 11 is in the medium-temperature state, the temperature sensor13 outputs “LH” as the temperature information STI.

When the memory cell array 11 is in the high-temperature state, thevoltage Vx is higher than the voltages Vr<0> and Vr<1> in FIG. 8. As aresult, both the outputs out<1> and out<0> become “high (H)”. Therefore,when detecting that the memory cell array 11 is in the high-temperaturestate, the temperature sensor 13 outputs “HH” as the temperatureinformation STI.

In response to “LL”, “LH”, or “HH” as the temperature information STIfrom the temperature sensor 13, the memory controller 20 controls thewrite operation and the read operation in accordance with “LL”, “LH”, or“HH”.

Moreover, the temperature sensor 13 only uses standard components in asemiconductor circuit, and therefore has an advantage of being easilyformable.

[2] Write Operation and Read Operation

FIGS. 10 and 11 are diagrams showing the write operation and the readoperation according to the embodiment. FIG. 12 is a diagram showing awrite operation and a read operation according to a comparative example.

First, the write operation and the read operation according to thecomparative example are described.

For example, in a memory cell including an MTJ element in an MRAM, whenthe memory cell is in a high-temperature state, the time required forwriting is short, but read disturb easily occurs in reading. On theother hand, when the memory cell is in a low-temperature state, theincidence of the read disturb in reading is low, but the time requiredfor writing is long.

Accordingly, in general, as shown in FIG. 12, a long write duration timetWR is set in writing on the assumption that the write duration time inthe low-temperature state is long, whereas a read duration time tRCD isset to a time including the ECC operation in reading on the assumptionthat the read disturb easily occurs in the high-temperature state.Therefore, the write duration time tWR and the read duration time tRCDare unnecessarily long.

Thus, the write operation and the read operation according to thepresent embodiment are performed as below.

When receiving temperature information STI1 (first information)indicating a high temperature from the temperature sensor 13, the memorycontroller 20 sets the write operation and the read operation in theMRAM 10 to a later-described operation in the high-temperature state.When receiving temperature information STI2 (second information)indicating a low temperature lower than the high temperature, the memorycontroller 20 sets the write operation and the read operation in theMRAM 10 to a later-described operation in the low-temperature state. Asdescribed above, the temperatures detected by the temperature sensor 13are the high temperature>the low temperature.

FIG. 10 shows the write operation and the read operation in thehigh-temperature state.

First, the write operation performed when the memory cell array 11 is inthe high-temperature state is described. Write data input from theinterface 14 is sequentially transferred to the page buffer 12D and thewrite buffer 12B, and written into the memory cell MC in the memory cellarray 11. In this case, writing into the memory cell MC is easy in thehigh-temperature state. That is, the magnetization direction of thestorage layer is inverted merely by passing a write current through theMTJ element RE included in the memory cell MC for a short time.

Thus, the memory controller 20 sets a time (write duration time tWRH)for passing the write current through the memory cell MC to be shorterthan the write duration time tWR, as shown in FIG. 10. For example, thewrite duration time tWRH is set to 12 clocks.

On the other hand, the read operation performed when the memory cellarray 11 is in the high-temperature state is as below. The word line WLis activated, and the memory cell MC is then selected, and a senseoperation is then performed for the selected memory cell by the senseamplifier 12A. The ECC operation for the read data is performed by theECC circuit 12C, and the read data is stored in the page buffer 12D. Thedata is further output to the outside from the page buffer 12D via theinterface 14. In the high-temperature state, a data error easily occursin reading, that is, the read disturb easily occurs, so that the ECCoperation is performed as described above for the read data read by thesense operation.

Thus, the memory controller 20 controls to perform the sense operation,the ECC operation, and the transfer to the page buffer 12D as the readoperation. Therefore, as shown in FIG. 10, the read operation requires atime (read duration time tRCDH) for the sense operation, the ECCoperation, and the transfer to the page buffer 12D. For example, theread duration time tRCDH is set to 13 clocks. The ECC operation is anoperation for detecting an error in read data and correcting the error.

FIG. 11 shows the write operation and the read operation in thelow-temperature state.

First, the write operation performed when the memory cell array 11 is inthe low-temperature state is described. Write data input from theinterface 14 is sequentially transferred to the page buffer 12D and thewrite buffer 12B, and written into the memory cell MC in the memory cellarray 11. In this case, writing into the memory cell MC is not easy inthe low-temperature state. That is, the magnetization direction of thestorage layer is not inverted unless a write current is passed throughthe MTJ element RE for a long time.

Thus, the memory controller 20 sets a time (write duration time tWRC)for passing the write current through the memory cell MC to be longerthan the write duration time tWRH as shown in FIG. 11. For example, thewrite duration time tWRC is set to 16 clocks.

On the other hand, the read operation performed when the memory cellarray 11 is in the low-temperature state is as below. The word line WLis activated, and the memory cell MC is then selected, and the senseoperation is then performed for the selected memory cell by the senseamplifier 12A. The read data is stored in the page buffer 12D. The datais further output to the outside from the page buffer 12D via theinterface 14. In the low-temperature state, the read disturb does noteasily occur in reading, so that the ECC operation does not need to beperformed for the read data read by the sense operation, in contrastwith the high-temperature state.

Thus, the memory controller 20 controls to perform the sense operationand the transfer to the page buffer 12D as the read operation.Therefore, as shown in FIG. 11, the read operation only requires a time(read duration time tRCDC) for the sense operation and the transfer tothe page buffer other than the ECC operation. The read duration timetRCDC is shorter than the read duration time tRCDH, and is set to, forexample, 9 clocks.

A temperature sensor which not only detects the high temperature and thelow temperature but also detects the medium temperature between the hightemperature and the low temperature as shown in FIGS. 8 and 9 may beused. When receiving temperature information STI3 (third information)indicating the medium temperature from this temperature sensor, thememory controller 20 sets the write duration time for passing the writecurrent through the memory cell MC to be longer than the write durationtime tWRH and shorter than the write duration time tWRC. When receivingthe third information STI3, the memory controller 20 may perform thesense operation, the ECC operation, and the transfer to the page buffer12D as the read operation, or may perform the sense operation and thetransfer to the page buffer 12D other than the ECC operation. Whether toperform the ECC operation is determined by the occurrence of the readdisturb.

The temperature information STI output from the temperature sensor 13 isalso input to the sense amplifier 12A, the write buffer 12B, the ECCcircuit 12C, the page buffer 12D, the interface 14, and the controller15. In response to the temperature information STI, the sense amplifier12A, the write buffer 12B, the ECC circuit 12C, the page buffer 12D, theinterface 14, and the controller 15 perform necessary operations inaccordance with this temperature information STI. For example, inaccordance with the temperature information STI, the ECC circuit 12Cpreviously performs a switch operation which occurs depending on whetherthe ECC operation is performed. Depending on whether the ECC operationis performed, it is necessary to change the timing for transferring theread data to the sense amplifier 12A, the ECC circuit 12C, the pagebuffer 12D, and the interface 14. Thus, the temperature information STIis also transmitted to the controller 15 so that the controller 15controls the timing for transferring the read data in accordance withthe temperature information STI.

[3] Advantageous Effects

As described above, when the memory cell is in the high-temperaturestate, the time required for writing is short, but the read disturbeasily occurs in reading. On the other hand, when the memory cell is inthe low-temperature state, the incidence of the read disturb in readingis low, but the time required for writing is long.

Accordingly, in general, a long write duration time is set in writing onthe assumption that the write duration time in the low-temperature stateis long, whereas the read duration time is set to the time including theECC operation in reading on the assumption that the read disturb easilyoccurs in the high-temperature state. Therefore, the times required forthe write operation and the read operation are unnecessarily long.

Under these circumstances, according to the present embodiment, thetemperature sensor which detects the temperature of the memory cell inthe memory cell array is provided, and the memory controller controlsthe write operation and the read operation in accordance with thetemperature information detected by the temperature sensor. In thehigh-temperature state, the time for passing the write current throughthe MTJ element in the memory cell is shortened to reduce the writeduration time. On the other hand, in the low-temperature state, the ECCoperation is eliminated from the read operation to reduce the readduration time. As a result, it is possible to reduce the times requiredfor the read operation and the write operation in the MRAM.

Although the MRAM that uses the magnetoresistive effect element has beendescribed as the resistance change memory by way of example in the aboveembodiment, the present embodiment is not limited thereto. The presentembodiment is also applicable to various kinds of semiconductor storagedevices including volatile memories and nonvolatile memories. Forexample, the present embodiment is also applicable to a resistancechange memory of the same kind as the MRAM, such as a resistive randomaccess memory (ReRAM) or a phase-change random access memory (PCRAM).

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel methods and systems describedherein may be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

What is claimed is:
 1. A resistance change memory comprising: a memorycell array comprising memory cells including magnetic tunnel junction(MTJ) elements; a write and read circuit which performs a writeoperation and a read operation for the memory cells; a temperaturesensor which outputs temperature information corresponding to atemperature of the memory cell array; and a memory controller whichcontrols the write operation and the read operation by the write andread circuit in response to the temperature information, such that afirst time period from a write command input to a pre-charge commandinput is variable according to the temperature information, while asecond time period from an active command input to the pre-chargecommand input is fixed constant regardless of the temperatureinformation.
 2. The resistance change memory according to claim 1,wherein: the temperature sensor outputs first information when thetemperature of the memory cell array is a first temperature, and thetemperature sensor outputs second information when the temperature ofthe memory cell array is a second temperature, and the memory controllersets a write duration time to write into the memory cells to a firstduration time when receiving the first information, and the memorycontroller sets the write duration time to a second duration time thatis longer than the first duration time when receiving the secondinformation.
 3. The resistance change memory according to claim 2,wherein the write duration time is a time to pass a write currentthrough the MTJ element.
 4. The resistance change memory according toclaim 1, wherein: the temperature sensor outputs first information whenthe temperature of the memory cell array is a first temperature, and thetemperature sensor outputs second information when the temperature ofthe memory cell array is a second temperature, and the memory controllersets a read duration time to read from the memory cells to a firstduration time when receiving the first information, and the memorycontroller sets the read duration time to a second duration time that isshorter than the first duration time when receiving the secondinformation.
 5. The resistance change memory according to claim 2,wherein: the temperature sensor outputs third information when thetemperature of the memory cell array is a third temperature that islower than the first temperature and that is higher than the secondtemperature, and the memory controller sets the write duration time to athird duration time that is longer than the first duration time and thatis shorter than the second duration time when receiving the thirdinformation.
 6. The resistance change memory according to claim 4,wherein: the temperature sensor outputs third information when thetemperature of the memory cell array is a third temperature that islower than the first temperature and that is higher than the secondtemperature, and the memory controller sets the read duration time to athird duration time that is longer than the first duration time and thatis shorter than the second duration time when receiving the thirdinformation.
 7. The resistance change memory according to claim 4,wherein: the read operation performed when the first information isreceived includes an error checking and correcting (ECC) operation todetect an error in read data read from the memory cells and correct theerror, and the read operation performed when the second information isreceived does not include the ECC operation.
 8. The resistance changememory according to claim 1, wherein the resistance change memorycomprises a magnetoresistive random access memory (MRAM).
 9. Theresistance change memory according to claim 1, wherein the first timeperiod and a third time period from an active command input to the writecommand input are both variable depending on the temperatureinformation, and wherein when the first time period increases accordingto the temperature information, the third time period decreases, andwhen the first time period decreases according to the temperatureinformation, the third time period increases.
 10. A resistance changememory comprising: a memory cell array comprising memory cells includingmagnetic tunnel junction (MTJ) elements; a write and read circuit whichperforms a write operation and a read operation for the memory cells; atemperature sensor which outputs temperature information correspondingto a temperature of the memory cell array; and a memory controller whichcontrols the write operation and the read operation by the write andread circuit in response to the temperature information, wherein: thetemperature sensor outputs first information when the temperature of thememory cell array is a first temperature, and the temperature sensoroutputs second information when the temperature of the memory cell arrayis a second temperature that is lower than the first temperature, whenreceiving the first information, the memory controller sets a writeduration time to write into the memory cells to a first duration time,and the memory controller sets a read duration time to read from thememory cells to a second duration time, when receiving the secondinformation, the memory controller sets the write duration time to athird duration time that is longer than the first duration time, and thememory controller sets the read duration time to a fourth duration timethat is shorter than the second duration time, and wherein a first timeperiod from a write command input to a pre-charge command input isvariable according to the temperature information, while a second timeperiod from an active command input to the pre-charge command input isfixed constant regardless of the temperature information.
 11. Theresistance change memory according to claim 10, wherein the writeduration time is a time to pass a write current through the MTJ element.12. The resistance change memory according to claim 10, wherein: thetemperature sensor outputs third information when the temperature of thememory cell array is a third temperature that is lower than the firsttemperature and that is higher than the second temperature, and thememory controller sets the write duration time to a fifth duration timethat is longer than the first duration time and that is shorter than thesecond duration time when receiving the third information.
 13. Theresistance change memory according to claim 10, wherein: the temperaturesensor outputs third information when the temperature of the memory cellarray is a third temperature that is lower than the first temperatureand that is higher than the second temperature, and the memorycontroller sets the read duration time to a fifth duration time that isshorter than the second duration time when receiving the thirdinformation.
 14. The resistance change memory according to claim 10,wherein: the read operation performed when the first information isreceived includes an error checking and correcting (ECC) operation todetect an error in read data read from the memory cells and correct theerror, and the read operation performed when the second information isreceived does not include the ECC operation.
 15. The resistance changememory according to claim 10, wherein the resistance change memorycomprises a magnetoresistive random access memory (MRAM).
 16. Theresistance change memory according to claim 10, wherein a first sum ofthe first duration time and the second duration time is same as a secondsum of the third duration time and the fourth duration time.
 17. Theresistance change memory according to claim 10, wherein the first timeperiod and a third time period from an active command input to the writecommand input are both variable depending on the temperatureinformation, and wherein when the first time period increases accordingto the temperature information, the third time period decreases, andwhen the first time period decreases according to the temperatureinformation, the third time period increases.
 18. A resistance changememory comprising: a memory cell array comprising memory cells includingresistance change elements; a write and read circuit which performs awrite operation and a read operation for the memory cells; a temperaturesensor which outputs temperature information corresponding to atemperature of the memory cell array; and a memory controller whichcontrols the write operation and the read operation by the write andread circuit in response to the temperature information, such that afirst time period from a write command input to a pre-charge commandinput is variable according to the temperature information, while asecond time period from an active command input to the pre-chargecommand input is fixed constant regardless of the temperatureinformation.
 19. The resistance change memory according to claim 18,wherein: the temperature sensor outputs first information when thetemperature of the memory cell array is a first temperature, and thetemperature sensor outputs second information when the temperature ofthe memory cell array is a second temperature that is lower than thefirst temperature, and the memory controller sets a write duration timeto write into the memory cells to a first duration time when receivingthe first information, and the memory controller sets the write durationtime to a second duration time that is longer than the first durationtime when receiving the second information.
 20. The resistance changememory according to claim 19, wherein the write duration time is a timeto pass a write current through the resistance change element.
 21. Theresistance change memory according to claim 18, wherein: the temperaturesensor outputs first information when the temperature of the memory cellarray is a first temperature, and the temperature sensor outputs secondinformation when the temperature of the memory cell array is a secondtemperature that is lower than the first temperature, and the memorycontroller sets a read duration time to read from the memory cells to afirst duration time when receiving the first information, and the memorycontroller sets the read duration time to a second duration time that isshorter than the first duration time when receiving the secondinformation.
 22. The resistance change memory according to claim 21,wherein: the read operation performed when the first information isreceived includes an error checking and correcting (ECC) operation todetect an error in read data read from the memory cells and correct theerror, and the read operation performed when the second information isreceived does not include the ECC operation.
 23. The resistance changememory according to claim 18, wherein the resistance change memorycomprises a magnetoresistive random access memory (MRAM).
 24. Theresistance change memory according to claim 18, wherein the first timeperiod and a third time period from an active command input to the writecommand input are both variable depending on the temperatureinformation, and wherein when the first time period increases accordingto the temperature information, the third time period decreases, andwhen the first time period decreases according to the temperatureinformation, the third time period increases.